A new type of laser which generates picosecond pulses is presented. 6 ps, ∼ 1 GW, 3 pps, m in a single pulse are obtained with good stability. Accurate timing of the pulses can be achieved, and no external pulse selection is required. In our laser, the pulse does not develop from quantum noise, but is the result of a nonlinear frequency and time processing in the cavity of a seed pulse that is coherent from the beginning of the shortening process. We believe that the remarkable characteristics of pulse stability are at least partially due to these considerations in coherence.